Fix can't change notification sound for work profile.

Use correct user id context to query the type,
so we won't get empty result unexpectedly.

If we get the null result, then we won't set sound sucessfully.

Fix: 233580016
Test: Manual test and set work profile sound works.
Change-Id: I7f8fb737a7c6f77a380f3f075a5c89a1970e39ad

src/com/android/settings/DefaultRingtonePreference.java

@@ -51,7 +51,7 @@ public class DefaultRingtonePreference extends RingtonePreference {
             return;
         }
 
-        String mimeType = getContext().getContentResolver().getType(ringtoneUri);
+        String mimeType = mUserContext.getContentResolver().getType(ringtoneUri);
         if (mimeType == null) {
             Log.e(TAG, "onSaveRingtone for URI:" + ringtoneUri
                     + " ignored: failure to find mimeType (no access from this context?)");

tests/unit/src/com/android/settings/DefaultRingtonePreferenceTest.java

@@ -59,6 +59,7 @@ public class DefaultRingtonePreferenceTest {
         when(mDefaultRingtonePreference.getRingtoneType())
                 .thenReturn(RingtoneManager.TYPE_RINGTONE);
         mDefaultRingtonePreference.setUserId(1);
+        mDefaultRingtonePreference.mUserContext = context;
     }
 
     @Test